JP5338764B2 - Toner for electrophotography and method for producing the same - Google Patents

Description

The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner capable of obtaining a good image in a small amount and a method for producing the same .

  Image formation by electrophotography is performed by developing and visualizing an electrostatic image with toner, transferring the obtained toner image onto a sheet, and then fixing it with heat and pressure. As the toner used for such image formation, a toner prepared by kneading a mixture of a binder resin and a colorant or a charge control agent, and adjusting the particle size distribution by pulverization is used.

  Conventionally, petroleum-derived resins such as styrene / acrylic resins and polyester resins have been used as binder resins. In recent years, in consideration of the environment, a method has been proposed in which a biodegradable resin having a low environmental impact at the time of disposal, or a biomass-derived resin made from renewable resources, is used as a toner resin. These biodegradable resins and biomass-derived plastics are called bioplastics and are expected to reduce the consumption of fossil resources and suppress the increase in the concentration of carbon dioxide in the atmosphere.

  One of the most promising resins among bioplastics is polylactic acid. Polylactic acid is a crystalline polyester having a melting point of about 170 ° C., a glass transition point of about 60 ° C., and a molecular weight of about 1 to 150,000. Currently, it is used for food packaging materials and containers. In addition, heat resistance and high durability have been added to polylactic acid, and it has also begun to be used for mobile phone cases and the like.

  However, when polylactic acid that is currently commercially available is used as it is as a resin for toner, there are problems that it is hard and has poor grindability, has a high softening temperature, and is not suitable for low-temperature fixing.

  In order to solve such a problem, proposals have been made to add a large amount of plant wax to polylactic acid (see, for example, Patent Document 1). However, in this proposal, it is possible to lower the softening temperature of the toner by adding a large amount of wax, but the toner easily aggregates due to the wax component, so that the productivity due to the lowering of the classification efficiency deteriorates. As the toner fluidity deteriorates, problems such as inferior toner transportability in the developing machine occur.

  There is also a proposal for blending two types of resins with different softening points into bioplastics for low-temperature fixability and fixing stability (see, for example, Patent Document 2). In this proposal, the low softening point resin serves as a bridge between the high softening point resin and the biodegradable resin, and the bioplastic is uniformly dispersed in the binder resin. However, the blending ratio of the bioplastic in the binder resin is about 13% by mass, and at most 33% by mass. Although there is no clear description, it is thought that one of the causes is that if the blending ratio of bioplastic is further increased, poor dispersion of bioplastic occurs and durability and pulverization deteriorate.

  As described above, there are many problems in using bioplastic as the main component of the binder resin of the toner, and even when a part of it is replaced, the blending amount is limited, and while maintaining good characteristics, It was desired that many biomass plastics could be blended.

  On the other hand, it is possible to lower the softening temperature and improve the grindability by hydrolyzing the bioplastic to reduce the molecular weight. However, when the durability of the toner using the bioplastic thus hydrolyzed was evaluated with an actual machine, it was found that there were problems such as fogging and a large amount of toner consumption.

Japanese Patent No. 2597452 Japanese Patent No. 3779221 JP 2006-91278 A

The present invention has been made under the circumstances as described above, and an object thereof is to provide an electrophotographic toner capable of obtaining a good image in a small amount and a method for producing the same.

In order to solve the above problems, a first aspect of the present invention is a bioplastic obtained by hydrolyzing a polylactic acid resin having a number average molecular weight of 100,000 or more and adjusting the number average molecular weight to 50,000. LR-147 (trade name, Nippon Carlit Co., Ltd.) as a charge control agent having a particle size of 500 nm or less crushed by a jet mill together with pulverizing silica to toner base particles containing a binder resin and a colorant comprising The toner for electrophotography is characterized in that 0.2 to 0.8 parts by mass are externally added to 100 parts by mass of the toner base particles.

In order to solve the above problems, a second aspect of the present invention is a bioplastic obtained by hydrolyzing a polylactic acid resin having a number average molecular weight of 100,000 or more and adjusting the number average molecular weight to 50,000. A raw material containing a binder resin and a colorant is melt-kneaded and pulverized to obtain toner base particles, and the obtained toner base particles are preliminarily crushed by a jet mill together with pulverization silica, and a particle size of 500 nm or less LR-147 (trade name, manufactured by Nippon Carlit Co., Ltd.) as a charge control agent is added to 0.2 to 0.8 parts by mass of 100 parts by mass of the toner base particles and mixed. An electrophotographic toner manufacturing method is provided.

  According to the present invention, an electrophotographic toner capable of obtaining a good image with a small amount is provided.

  Hereinafter, embodiments of the present invention will be described.

  As a result of intensive investigations to solve the problems of toners using bioplastics whose pulverizability is improved by hydrolyzing and lowering the softening point, the inventors of the present invention have found that a charge control agent has been added during toner production. It has been found that it is possible to prevent fogging and increase in toner consumption by externally adding a predetermined amount of a charge control agent to toner fine particles, rather than kneading with a resin or the like.

  That is, in the electrophotographic toner according to an embodiment of the present invention, the charge control agent is added to the toner base particles containing the binder resin made of bioplastic and the colorant, with respect to 100 parts by weight of the toner base particles. To 0.8 parts by mass.

  When the external addition amount is less than 0.2 parts by mass, the effect of adding the charge control agent cannot be obtained, and the fogging and image density stability are not improved. Further, when the amount of external addition exceeds 0.8 parts by mass, the fog is not particularly improved.

  JP-A-2009-230065 proposes to externally add a charge control agent to toner base particles using a normal binder resin that is not a bioplastic, but consideration is given to the amount of charge control agent added. However, if the charge control agent with the stated addition amount is externally added to the toner base particles using bioplastic as a binder resin, fog is likely to occur and there is a problem in image density stability. I know that there is.

  As a method for externally adding the charge control agent, a method of strongly stirring the base toner and the charge control agent in a mixer is usually used. However, since the charge control agent usually does not exist as primary particles and aggregates to a particle size of about 10 μm, when the toner base particles are subjected to external addition treatment, the charge control agent particles In some cases, it is difficult to firmly adhere to the surface of the toner base particles. If the charge control agent is not firmly attached to the toner base, the toner will be released from the toner base when the toner receives a shearing force in the developing tank during printing, and normal frictional charging will not be performed. The chargeability is lowered, and the image is likely to be fogged.

  Therefore, it is desirable to finely pulverize (crush) the charge control agent before external addition. As for the fine pulverization of the charge control agent, for example, as described in JP-A-2009-230065, the charge control agent is previously crushed silica having a particle size of 20 nm or less (based on 100 parts by mass of the charge control agent). By mixing with 0.5 to 10 parts by mass of silica) and a Henschel mixer and pulverizing with a jet mill, it can be finely pulverized to 500 nm or less. If the charge control agent is crushed alone, it may be difficult to make the particle size small enough to firmly adhere to the surface of the toner base particles, and the charge control agent particles may be uniformly distributed on the surface of the toner base particles. It may be difficult to adhere.

  Thus, the mixture obtained by adding silica to the charge control agent is pulverized by a jet mill to obtain a charge control agent having an average particle size of 500 nm or less, so that the charge control agent particles are uniformly distributed on the surface of the toner base particles. It becomes possible to adhere firmly.

  A jet mill is a pulverizing apparatus that pulverizes an object to be processed with a high-pressure, high-speed gas ejected from a nozzle. In this embodiment, the jet mill can be used for pulverizing a charge control agent. The charge control agent applied to the jet mill together with the silica is accelerated by a high-pressure and high-speed gas, for example, air, and is crushed by the collision of the particles, or by the collision with the collision plate.

  As the charge control agent used in the present embodiment, a resin containing a quaternary ammonium salt or an amino group as a positive charge control agent, a metal complex of salicylic acid, a metal of benzyl acid as a negative charge control agent Examples include complex salts, calixarene-based phenol condensates, and resins containing carboxy groups. More specifically, for example, alumina such as LR-147, E-89, E-84 (all trade names) can be preferably used.

  Examples of the bioplastic used in the present embodiment include polyhydroxybutyrate, poly (hydroxybutyrate / hydroxyhexanoate) as a microbial production system, esterified starch, cellulose acetate, chitosan as a natural product system, Examples of the chemical synthesis system include polylactic acid, polycapacactone, polybutylene succinate, polyvinyl alcohol, polyglycolic acid, etc., but it is more preferable that the raw material is a renewable biomass, and it is industrially produced. It is preferable from the viewpoint of versatility and price. Specifically, polylactic acid is most preferable.

  The method for producing the bioplastic used in the present embodiment is not particularly limited, and a conventionally known method can be used. Among them, polylactic acid is fermented with starch such as corn as a raw material to obtain lactic acid, followed by dehydration condensation directly from lactic acid monomer, or ring opening in the presence of a catalyst through cyclic dimer lactide from lactic acid. There is a method of synthesis by polymerization. There are optical isomers in lactic acid, and there are L-lactic acid and D-lactic acid, and any of these lactic acids may be used alone or in a mixture.

  The commercially available polylactic acid is synthesized by a ring-opening polymerization method for obtaining a higher molecular weight polylactic acid for reasons such as improving heat resistance, and its number average molecular weight is 100,000. The above is the mainstream. Since polylactic acid having a high molecular weight has a high softening point and poor grindability, hydrolyzing polylactic acid reduces the molecular weight of polylactic acid, resulting in a toner resin having good grindability and fixability. It is desirable to do. Here, the molecular weight of the polylactic acid preferably used in this embodiment is about 5,000 to 50,000.

  As a method for hydrolyzing polylactic acid, there is a method of treating polylactic acid at high temperature and high humidity, for example, at a temperature of 80 ° C. and a humidity of 80% RH. As a result, hydrolysis of polylactic acid occurs, the molecular weight decreases, and polylactic acid having an appropriate softening temperature and good grindability as a resin for toner can be obtained in several tens of hours. As another method, there are a method using heated steam, and a method of performing hydrolysis by melt-kneading polylactic acid and water.

  As the colorant used in the toner according to the exemplary embodiment, a conventionally known colorant can be used. For example, carbon black as a black colorant, CIPigment Blue 15: 3 as a blue colorant, CIPigment Red 57: 1,122,269 as a red colorant, and CIPigment as a yellow colorant Yellow 74,180,185 and so on. In consideration of the influence on the environment which is one of the objects of the present invention, a single colorant having high safety is preferable.

  The content of these colorants is preferably 1 to 10% by mass as a whole toner. Moreover, you may use the masterbatch which disperse | distributed resin and a coloring agent in high concentration previously as a coloring agent.

  Examples of the release agent used in the toner according to the exemplary embodiment include olefin waxes such as polypropylene wax, polyethylene wax, and Fischer Tropsch wax, natural waxes such as carnauba wax, rice wax, and scale insect wax, and synthetic ester waxes. Is mentioned. In order to improve low-temperature fixability and high-speed printing performance, it is preferable that the release agent has a relatively low melting point of 60 to 100 ° C. Specifically, natural carnauba wax is used in consideration of environmental effects. More preferred. The release agent is preferably 1 to 10% by mass based on the whole toner.

  A known toner resin can be added to the toner according to the exemplary embodiment as necessary. Examples thereof include styrene / acrylic resins and polyester resins. Polyester resins developed for toners are preferred from the viewpoints of pigment dispersibility and low-temperature fixability. Resin may be individual or may mix 2 or more types. Considering the influence on the environment, which is one of the objects of the present invention, the total toner content is preferably 0 to 50% by mass.

  As other materials, a low molecular resin can be added to improve grindability and fixability. Here, as the low molecular resin, there are rosin and rosin derivatives, polyterpene resins, terpene phenol resins, petroleum resins, and the like that are commercially available as tackifiers, which are resins in the oligomer region having a molecular weight of several hundred to several thousand.

  A conventionally known hydrolysis inhibitor can be added to the toner according to the exemplary embodiment as necessary. Examples thereof include carbodiimide compounds, isocyanate compounds, oxazoline compounds, and the like. Such a hydrolysis inhibitor is capable of inhibiting the chain reaction of hydrolysis by sealing the residual monomer and the hydroxyl group or carboxyl group terminal generated by the decomposition.

  As the hydrolysis inhibitor, “carbodilide LA-1” manufactured by Nisshinbo Co., Ltd., which is a polycarbodiimide compound, is commercially available. The addition amount of the hydrolysis inhibitor is preferably 0.01 to 10% by mass and more preferably 0.05 to 5% by mass with respect to the bioplastic.

  A known crystal nucleating agent can be added to the toner according to the exemplary embodiment as necessary. Examples of the crystal nucleating agent include inorganic nucleating agents such as talc, organic carboxylic acid metal salts such as sodium benzoate, phosphoric acid ester metal salts, pendylidene sorbitol, carboxylic acid amides, and the like.

  The toner according to the exemplary embodiment containing each of the above components as a raw material can be manufactured by a conventionally known manufacturing method.

  For example, first, a raw material mixture containing a bioplastic, a colorant, a release agent and the like is mixed by a mixer. As a mixing machine, arbitrary things, such as a Henschel mixer, a super mixer, a V-type blender, and a Nauta mixer, can be used.

  Next, the mixed raw material mixture is supplied to a kneader, where it is melt-kneaded. As the kneading machine, any type of extrusion kneading machine such as a twin-screw extrusion kneading machine and a single-screw extrusion kneading machine, an open roll type kneading machine such as a continuous two-roll mill, a continuous three-roll mill, and a batch roll mill can be used. Things can be used.

  The melt-kneaded product discharged from the kneader is usually cooled, pulverized, and classified according to a method used for toner production to obtain a toner particle matrix having a predetermined average particle diameter. The cooling means, the pulverizing means, and the classification means are not particularly limited, and those usually used for toner production can be employed. For example, a cooling means by rolling or blowing an air flow can be used for cooling, and an airflow pulverizer such as a collision plate pulverizer can be used for pulverization, and various airflow classifiers can be used for classification. Can be used. Here, the particle size of the toner particle matrix is usually adjusted to be about 5 to 10 μm.

  The toner particle matrix thus obtained is externally added with a charge control agent and silica. It is desirable to use the charge control agent that has been crushed as described above. An electrophotographic toner can be obtained by adding the pulverized charge control agent together with other external additive silica (external additive silica) to the toner particle base, and mixing and stirring.

  Examples of the present invention and comparative examples will be shown below to describe the effects of the present invention more specifically. As the charge control agent used in Examples and Comparative Examples, a finely pulverized one as described below was used, and a polylactic acid obtained by hydrolyzing a commercially available polylactic acid as described below was used.

<Fine grinding of charge control agent>
In advance, 100 parts by mass of the charge control agent and 0.1 to 10 parts by mass of the pulverizing silica were mixed with a Henschel mixer and pulverized with a jet mill to obtain finely pulverized charge control agent fine particles. Using an IDS-2 type manufactured by Nippon Pneumatic Industry Co., Ltd. as a pulverizer, pulverization was performed at a pressure of 0.6 MPa and a feed amount of 3 kg / h. Table 1 below shows the types of charge control agents used.

<Production of low molecular weight polylactic acid>
Polylactic acid “REVODE101B” manufactured by Kaisei Biological Co., Ltd. is placed in a constant temperature and humidity chamber set at a temperature of 80 ° C. and a humidity of 80% RH, and is hydrolyzed by changing the treatment time. Lactic acid was obtained.

Table 2 below shows the hydrolysis treatment time and the molecular weight of the hydrolyzed polylactic acid.

  As shown in Table 2 above, it can be seen that the molecular weight of the hydrolyzed polylactic acid decreases as the treatment time increases.

  The measuring method of each physical property value is shown below.

<Toner particle size measurement>
A small amount of toner, purified water, and a surfactant are put into a beaker, and this is dispersed with an ultrasonic cleaner to obtain a sample toner. The toner particle size is measured using Multisizer II (manufactured by Coulter, Inc.) as an apparatus. The measurement is performed with an aperture of 100 μm and a count of 50,000, and a volume average particle diameter is obtained.

<Measurement of molecular weight>
The molecular weight Mn is a number average molecular weight measured by GPC (gel permeation chromatography) using a calibration curve prepared with a polystyrene sample having a known molecular weight as a standard. As a measuring device, GPC (manufactured by Shimadzu Corporation) and detector Rl are used.

<Measurement of particle size of charge control agent>
A small amount of a charge control agent, purified water, and a surfactant are placed in a beaker, and this is dispersed with an ultrasonic cleaner to obtain a dispersion. The particle diameter of the charge control agent is measured using a laser diffraction particle diameter measuring apparatus LA-920 (manufactured by Horiba, Ltd.) as an apparatus. The measurement is determined by the volume average particle size.

Example 1
89 parts by mass of polylactic acid (molecular weight 50,000) having a reduced molecular weight as a binder resin, 4 parts by mass of carbon black (manufactured by CABOT Co., Ltd .: MOGUL L) as a colorant, and Carnauba wax No. 1 powder as a release agent 6 parts by mass (manufactured by Nippon Wax Co., Ltd.) was put into a Henschel mixer (manufactured by Mitsui Mining Co., Ltd., using standard blades) and mixed.

  The obtained mixture was melt-kneaded with a twin screw extruder (screw diameter: 43 mm, L / D = 34), cooled, and coarsely crushed with a Rotoplex (2 mm screen manufactured by Hosokawa Micron Corporation), and then an impact plate crusher (Nippon Pneumatic Industry Co., Ltd. IDS-2) and wind classifier (Nippon Pneumatic Industry Co., Ltd. DSX-2) were pulverized and classified so that the average particle size of the toner was 9.0 μm. To obtain fine particles.

  To 100 parts by mass of the obtained fine particles, 0.5 parts by mass of the charge control agent fine particles CCA-1 shown in Table 1 prepared in advance are added, and 2 with a Henschel mixer (made by Mitsui Mining Co., Ltd., using standard blades). After mixing for 5 minutes, “RY-200” (manufactured by Nippon Aerosil Co., Ltd., hydrophobic silica: primary particle size 12 nm) was mixed for 3 minutes as a fluidity adjusting agent to obtain a toner.

Examples 2 to 7
As shown in Table 3 below, a toner was prepared in the same manner as in Example 1 except that the type and amount of charge control agent fine particles were changed.

Comparative Example 1
89 parts by mass of polylactic acid (molecular weight 50,000) having a reduced molecular weight as a binder resin, 4 parts by mass of carbon black (manufactured by CABOT Co., Ltd .: MOGUL L) as a colorant, and Carnauba wax No. 1 powder as a release agent ( Charge 6 parts by mass of Nippon Wax Co., Ltd. and 1 part by mass of LR-147 (Nihon Carlit Co., Ltd.) as a charge control agent into a Henschel mixer (Mitsui Mine Co., Ltd., using standard blades). , Mixed.

  The obtained mixture was melt-kneaded with a twin screw extruder (screw diameter: 43 mm, L / D = 34), cooled, and coarsely crushed with a Rotoplex (2 mm screen manufactured by Hosokawa Micron Corporation), and then an impact plate crusher (Nippon Pneumatic Industry Co., Ltd. IDS-2) and wind classifier (Nippon Pneumatic Industry Co., Ltd. DSX-2) were pulverized and classified so that the average particle size of the toner was 9.0 μm. Thus, toner fine particles were obtained.

  The toner fine particles were mixed with “RY-200” (manufactured by Nippon Aerosil Co., Ltd., hydrophobic silica: primary particle size 12 nm) as a fluidity adjusting agent for 3 minutes to obtain a toner.

Comparative Example 2
A toner was prepared in the same manner as in Comparative Example 1 except that Bontron E-84 (manufactured by Orient Chemical Co., Ltd.) was used instead of the charge control agent LR-147 used in Comparative Example 1.

Comparative Example 3
A toner was prepared in the same manner as in Comparative Example 1 except that Bontron E-89 (manufactured by Orient Chemical Co., Ltd.) was used instead of the charge control agent LR-147 used in Comparative Example 1.

Comparative Example 4
A toner was produced in the same manner as in Example 1 except that the amount of the charge control agent used in Example 1 was changed to 1.0 part by mass.

Comparative Example 5
A toner was prepared in the same manner as in Example 1 except that the amount of the charge control agent used in Example 1 was changed to 0.1 parts by mass.

Comparative Example 6
A toner was prepared in the same manner as in Example 6 except that the amount of the charge control agent used in Example 1 was changed to 1.0 part by mass.

Comparative Example 7
A toner was prepared in the same manner as in Example 7, except that the amount of the charge control agent used in Example 1 was changed to 1.0 part by mass.

  The toners of Examples 1-7 and Comparative Example 1-7 prepared as described above were converted into non-magnetic one-component developing printer “Casio Page Presto N-5” (manufactured by Casio Computer Co., Ltd .: 29 color prints per minute ( A4 horizontal), mounted at a process speed of 129 mm / s), and in normal environment (25 ° C, 50% RH), using plain paper (XEROX-P paper A4 size) with 5% printing and solid printing every 2000 sheets Two sheets and two blank sheets were printed, and thereafter four times (a total of 10,000 sheets of 5% printing) was repeated.

Test 1 (fogging evaluation)
After completing 5% printing for 10,000 sheets, blank paper printing was performed, and the printing was forcibly terminated by opening the front door during printing. The fog toner on the OPC drum at that time was copied with a mending tape and pasted on a white paper. A mending tape with nothing was affixed to a blank sheet and compared.

  The measurement was evaluated as follows using the difference in presence or absence of fog toner as the fog value from the Z value of the XYZ coordinates obtained using a spectral color difference meter “SE-2000” manufactured by Nippon Denshoku Co., Ltd.

◎: Fog value less than 2 is good ○: Fog value is better than 2 and less than 5 △: Fog value is more than 5 and less than 10 and practically acceptable level ×: Fog value is more than 10 and bad Test 2 (Image density stable) sex)
The image density was measured at five points at the center and four corners of a solid image printed every 2000 sheets. In the measurement, the image density was measured using X-rite 938 manufactured by X-rite Co., Ltd., and the average density of 5 points was determined. The image density stability was determined from the maximum value and the minimum value at each sampling point according to image density stability (%) = (minimum image density / maximum image density) × 100.

◎: Image density stability is 95% or more, good ○: Image density stability is 85% or more, good △: Image density stability is 75% or more, and there is no practical problem ×: Image density stability is less than 75% Test 3 (storability)
10 g of the toner was put in a glass beaker and left in a constant temperature and humidity chamber at 50 ° C. and 90% RH for 8 hours, and then the cohesiveness of the toner was visually confirmed.

(Evaluation criteria)
A: No aggregation of toner is observed. O: Almost no aggregation of toner is observed. Δ: A slight aggregation of toner is observed. X: Aggregation of toner is observed. Test 4 (fixing property)
The fixing part was modified so that the temperature of the fixing part of “Casio Page Presto N-5” (manufactured by Casio Computer Co., Ltd .: process speed 129 mm / sec) could be varied, and used as a fixing tester.

  The fixing temperature of the upper fixing roll was varied in the range of 100 to 200 ° C. every 10 ° C., a solid image was printed, the cold offset and hot offset of the image were visually evaluated, and the non-offset area was obtained and evaluated. .

The paper used was P paper A4 size (64 g / m ² ) manufactured by XEROX Corporation. The oil supply roller of the fixing device was removed.

(Evaluation criteria)
◎: Non-offset region is 30 ° C or higher ○: Non-offset region is 20 ° C
Δ: Non-offset region is 10 ° C
×: No non-offset area Test 5 (toner consumption)
Toner consumption was measured in a 10,000 sheet test with 5% printing.

(Evaluation criteria)
◎: Toner consumption is 100% or less compared to genuine toner ○: Toner consumption exceeds 100% and less than 103% compared to genuine toner △: Toner consumption exceeds 103% compared to genuine toner 106% or less ×: The toner consumption exceeds 106% compared with genuine toner. Table 3 shows the test results of the toners of Example 1-7 and Comparative Example 1-7.

  From Table 3 above, the following can be understood. That is, toners (Examples 1 to 7) obtained by externally adding 0.2 to 0.8% by mass of a charge control agent to a toner particle matrix using bioplastic as a binder resin are fogging, image density stability, Good results are shown in all of storability, fixability, and toner consumption.

  In contrast, the toners of Comparative Examples 1 to 3 in which a charge control agent is internally added are particularly inferior in image stability. In addition, the charge control agent is too small as 0.1% by mass (Comparative Example 5) or too much as 1% by mass (Comparative Examples 4, 6, and 7). Absent.

Claims (2)

To toner base particles containing a binder resin and a colorant made of a bioplastic obtained by hydrolyzing a polylactic acid resin having a number average molecular weight of 100,000 or more and adjusting the number average molecular weight to 50,000 , LR-147 (trade name, manufactured by Nippon Carlit Co., Ltd.) as a charge control agent having a particle size of 500 nm or less crushed by a jet mill together with pulverization silica was added in an amount of 0.2 to 100 parts by mass of the toner base particles. An electrophotographic toner comprising 0.8 part by mass externally added. After melt-kneading a raw material containing a binder resin made of bioplastic obtained by hydrolyzing a polylactic acid resin having a number average molecular weight of 100,000 or more and adjusting the number average molecular weight to 50,000, and a colorant The toner base particles were pulverized to obtain LR-147 (trade name, Nippon Carlit (trade name ) as a charge control agent having a particle diameter of 500 nm or less, which was previously pulverized by a jet mill together with silica for pulverization. the Ltd.)), the electrophotographic method for producing a toner, characterized in that to produce the toner base particles 100 parts by mass with respect to 0.2 0.8 mass externally added and mixed to.